In recent years, trends toward the provision of vegetables that children can easily eat or the intake of raw vegetables by health-conscious consumers become popular, and an attempt of improvement of vegetable varieties is made to satisfy such needs. However, vegetables, such as plants of the genus Allium, in particular, onions, are difficult to eat raw because of distinctive pungency.
The lachrymatory factor (LF) serving as a pungent component and also as a lachrymatory component of an onion are found to be generated by the reaction mechanism shown below, which proceeds upon cutting or breaking of raw onion tissue (Imai S. et al., An onion enzyme that makes the eyes water, Nature, 419, 685, 2002).

When onion cell is broken upon cooking or processing, specifically, trans-1-propenyl cysteine sulfoxide (PRENCSO) as a substrate is degraded by alliinase, and sulfenic acid (1-propenyl sulfenic acid), pyruvic acid, and ammonia are generated in an amount of a molecule each from a molecule of PRENCSO. The generated sulfenic acid is then converted into a lachrymatory factor (LF, propanethial-S-oxide) as a pungent component by lachrymatory factor synthase (LFS).
In Japan, there is a very early maturing variety of an onion with low pungency, which is referred to as “spring onion.” In a very early maturing onion variety, moisture content is high and the amount of dry matter is low. The PRENSCO concentration is lowered and the amount of a pungent component (a lachrymatory factor) generated is reduced because of the features described above. While pungency of a very early maturing onion variety is low, it yields some pungency. Accordingly, it is necessary to immerse an onion in water when it is to be eaten raw. In addition to a labor required for immersion of an onion in water, nutritious components would be lost due to immersion. Also, the storage stability of the variety indicated above is poor and, disadvantageously, such variety can be provided only at the limited time.
As a technique of producing a variety with low pungency, a technique of regulating fertilization to reduce the amount of a substrate serving as an origin of pungency has been employed. However, such substrate is not completely eliminated by the technique, and, in general, pungency would not be reduced to an extent that pungency is not sensed when an onion is eaten raw.
In addition, onions with reduced pungency have heretofore been developed and reported. JP 2009-501528 A discloses long-day onions having low pungency and the amount of pyruvic acid generated when the onion tissues are broken is 3.0 to 5.5 μmol/g. JP 2011-510618A also discloses long-day onions having low pungency and the amount of pyruvic acid generated when the onion tissues are broken is 2.5 to 5.5 μmol/g FW. While the onion varieties disclosed therein exhibit low pungency, such onions are not completely free of pungency. Accordingly, it is necessary to immerse such onions in water when they are to be eaten raw.
Accordingly, onions with very weak or no pungency and tear-inducing property are still desired in the art.